1. Field
This invention relates to the field of apparatuses in which a piston in a cylinder is advanced to force contents of the cylinder out of the cylinder. More specifically it is in the field of drywall construction apparatus incorporating a cylinder and piston with the piston being mechanically advanced to force contents of the cylinder out of the cylinder. Still more specifically it is in the field of automatic tapers used in drywall construction, such automatic tapers having a cylinder and a piston in that cylinder mechanically advanced to dispense taping compound known as mud onto a Joint between drywall panels being taped.
2. Prior Art
The direct prior art to the subject invention is formed in the automatic tapers marketed by Ames Drywall Systems, Inc. in the United States and Concorde Tool Company, Inc. in Canada. In such tools a roller assembly at the dispensing end of the tool is pressed against and rolled along the work surface. The roller pulls tape off a roll of tape on the cylinder/handle of the tool and a spool, clutch driven by the roller, reels in a cable to pull the piston through the cylinder to dispense mud onto the tape being applied. As the piston comes near to the end of the cylinder, mechanism declutches the spool from the roller and intermediate drawing mechanism so that the cable will not be strained or broken when the piston can move no farther. Service records of these tools clearly indicate that the piston advance mechanism is unduly prone to fail and/or malfunction and that time and cost to service and repair the mechanism are undesirably high. Also, the amount of piston advance and resultant quantity of mud dispensed per unit of travel of the taper head is not adjustable. Accordingly, the prime objective of the subject invention is to provide a piston advance mechanism for automatic tapers which is more durable and easier and less costly to service than conventional piston advance mechanisms. Another objective is that the mechanism be adjustable to control the ratio of piston advance to advancement of the taper in use.